I had that happen sometimes during my first playthrough but it was rare. My build had 18 to 20 INT, I used Legendary Ping, I had crit perk but... when it happened it might have been when I took down a lot of enemies instantly or in very short sequence. But that was over 7 months ago and only thing I can say for sure, is that I remember those enemies whom were standing still being anomaly, I remember them for that reason.
Now on my second playthrough I finished week ago or so, I think it might happened once or twice, but this time my build had INT 14, so I don't think I actually had quickhacking crit perk.
This sounds like a good idea. What comes to performance (as I'm on Xbox One X too) it would make sense to me, that there are priorities, like maintaining certain FPS and animations, like falling down, has certain window where it gets executed if there's CPU/GPU resources available, could be sound effects too, anything and if there isn't animations simply won't play. Doesn't really matter, for my big relief that I can be completely out in the woods here, but it doesn't really matter as we can't really do anything about it.
Anyway, who I think it may be something like that, is because sometimes regardless of approach, guns, melee, quickhaking, anything but take downs, it happens that enemy NPC falls, and then sometimes later, it falls again. It might be that there's no sound effect, like "aaaargh!" when it falls first time, but then on second time it goes through falling animation there maybe sound but can't say for sure.
What can be said for sure, it's not intended and IMO best thing to do is to report it via support site, so they are aware and get a picture of how many players experience it.
